Physical inactivity, low physical fitness, and tobacco and alcohol use are known to be prevalent in adolescent youth. These problematic health behaviors and characteristics tend to develop during early adolescence. This investigation examines the effects of an after-school/summer physical activity promotion program on physical activity, behavioral determinants of physical activity participation, physical fitness, and tobacCo and alcohol use in adolescent youth. A quasi-experimental research design will be employed and the effects of the intervention will be measured in all public school students, initially in the 5th grade (N = approximately 250), in a rural predominantly African-American community in South Carolina. All students at the same grade level in the public schools in a comparable community will serve as controls (N = approximately 300). Dependent variables and key intervening variables will be measured during the latter halves of the 5th, 6th and 7th grade years in students in the intervention and control groups. The intervention program will be delivered during a 19 month period extending from the summer following the 5th grade year through the fall semester of the 7th grade year. The intervention program is based on Pender's Health Promotion Model and emphasizes enhancement of self-efficacy, a cognitive perceptual factor in the model. Older teenagers will Complete an extensive preparatory course and will serve as program leaders in the after-school/summer intervention program. This study will provide important information on promotion of physical activity and physical fitness in disadvantaged adolescent youth and will determine the extent to which delivery of such a program can affect avoidance of problematic health behaviors such as tobacco and alcohol use.